Research On Creep Properties Of Micro-solder Joints Under Thermo-electric Action

As electronic technology continue to move toward higher density and higher reliability,the size of solder joints and interconnect pitches continue to decrease.Under normal service conditions,the micro-solder joints will be affected by various loads such as heat,electricity,and force,which will lead to reliability problems of the package structure.In this paper,the effects of intermetallic compound(IMC)proportion,solder joint shape and thermo-electric coupling pretreatment on the creep properties of copper pillar microbumps were studied,and the corresponding failure modes and mechanisms were analyzed.The main contents of this article include:(1)Solder joints with different IMC thicknesses were obtained by adjusting the bonding parameters during the thermocompression bonding process,and the growth law of the IMC during the thermocompression bonding process was analyzed.The barrel-shaped,cylindrical and hourglass-shaped solder joints were obtained by controlling the solder joint gap.Finally,the effect of IMC and solder joint shape on its shear strength was studied.(2)Creep experiments were carried out on cylinder-shaped solder joints with different IMC thicknesses under different stress conditions.The results show that with the increasing stress,the steady-state creep strain rate of all solder joints increases continuously,and the fracture position of the solder joints gradually approaches the interface between the solder and the copper column.With the increase of IMC thickness,the steady-state creep strain rate of solder joints showed a trend of first decreasing and then increasing.(3)Creep experiments were carried out on solder joints with different shapes under different temperature and stress conditions.Under different experimental conditions,all three solder joints showed typical creep characteristics,and their steady-state creep strain rates increased with the increase of temperature and shear stress.Under the same conditions,the steady-state creep rate of the hourglass-shaped solder joint is always higher than that of the other two solder joints.Finally,the creep deformation behavior of the solder joints is characterized by the Garofalo hyperbolic sine creep constitutive equation.(4)The thermo-electric coupling experiment and the finite element simulation are carried out on the solder joints with different shapes.The results show that the anti-electromigration ability of the hourglass-shaped solder joint is the worst,while that of the cylinder-shaped solder joint is the highest.In addition,creep experiments were carried out on three solder joints with thermo-electric coupling pretreatment for 10 h and 40 h.It was found that with the increase of thermo-electric coupling pretreatment time,the steady-state creep strain rate of solder joints increased significantly,and the fracture mode of solder joints gradually changed from ductile to brittle fracture.Among the three types of solder joints,the creep resistance of the hourglass-shaped solder joints is greatly affected by the thermo-electric coupling pretreatment.